In pressurized water reactors, ion exchange resins are used to purify the water used in the primary loop of the reactor. After a period of time, the ion exchange resin becomes contaminated with radioactive and other contaminants and must be disposed of. The primary loop of the reactor also contains boric acid which absorbs neutrons, converting their kinetic energy into heat, and the boric acid solution must also be disposed of from time to time for various reasons.
The Nuclear Regulatory Commission (NRC) requires that these low level radioactive wastes be converted into a free-standing monolith for transportation and disposition. It has been the practice in the industry to mix the boric acid solution with the ion exchange resins, to eliminate the need to add clean water to the resins, and then to convert the mixture into a solid monolith by adding cement. However, if the boric acid concentration is less than about 30% by weight a soft, pasty composition is initially produced that must be stored for several months until it solidifies. This greatly adds to the cost of disposing of these waste products.